1. Field of the Invention
This invention relates to packaging. More specifically, the invention relates to a multi-sided container or box made of corrugated paperboard. In particular, the invention relates to a corrugated paperboard tray for containing poultry products, wherein the tray has improved stacking strength and resistance to distortion from lateral forces applied to the sides or ends of the tray.
2. Prior Art
Various styles of paperboard boxes are known in the prior art for containing a variety of products. Conventional boxes may have four sides and be square or rectangular in plan view, or they may have eight sides, with opposed pairs of parallel side and end walls and diagonal corner panels oriented at 45xc2x0 to the longitudinal axis of the box and connecting adjacent side and end walls.
Examples of prior art eight sides boxes or trays are disclosed in applicant""s prior U.S. Pat. Nos. Des.361,892 and 5,752,648. These boxes are designed for containing poultry pieces packed in ice, and are usually termed poultry trays. They are formed from a unitary blank of corrugated paperboard, and are sometimes coated on both sides with wax or other material to impart rigidity and resistance to water degradation. The diagonal corner panels subtend an angle of 45xc2x0 with respect to the longitudinal axis of the box.
Eight sided trays have greater compressive strength when stacked on top of one another, and exhibit less side wall bulge from the weight of the contents therein, than do four sided trays. However, because of the diagonally oriented corner panels, an eight sided tray tends to flex or distort, especially at the open top edge, when lateral force is applied to the sides or ends of the tray, as occurs for example when two eight sided trays are pushed together end-to-end during stretch wrapping of the trays to form a unit load. This distortion of the tray can result in dislodgement of the cover which is usually applied to the tray, or make it difficult to apply a cover. Additionally, these changes in dimension of the tray may cause other difficulties when the trays are palletized during shipment and/or storage. Additionally, there are no square corners on an eight sided tray around which a label can be wrapped so that it is visible from each of two adjacent sides.
Accordingly, there is need for a tray that has superior stacking strength and resistance to distortion when transverse forces are applied to the ends or sides of the tray.
The tray of the invention has stacking strength superior to a four sided container, and resistance to distortion superior to an eight sided container when transverse forces are applied to the ends of the tray.
In one embodiment of the invention, for a tray having diagonal corner panels, the diagonal corner panels are oriented from about 35xc2x0 to about 40xc2x0, and in a preferred embodiment 38xc2x0, with respect to the longitudinal axis of the tray. The shallower angle of the corner panels, compared with the conventional 45xc2x0 angle, changes the resultant force vector slightly toward the ends of the tray, increasing resistance to distortion from force applied to the ends of the tray. The shallower angle of the corner panels also results in wider corner panels and concomitant shorter side panels, with comparable or even improved stacking strength over similarly sized eight sided trays with the diagonal corner panels oriented at 45xc2x0. These beneficial results are obtained in trays having six, seven or eight sides, for example, with two, three or four diagonal corner panels, respectively.
In an alternate embodiment, for a tray having diagonal corner panels, at least one corner of the tray is squared. Thus, an eight sided tray, for example, is modified to have one square corner, producing a seven sided tray, or two diagonally opposite corners are made square to produce a six sided tray. The remaining diagonal corner panels may be oriented at any angle, including 38xc2x0 or 45xc2x0 relative to the longitudinal axis of the tray, although if oriented at 38xc2x0 some of the benefits discussed above can be additionally obtained. Although the seven sided tray resists distortion caused by lateral force applied to the side or end of the tray, the resistance is not as great as that provided by the six sided tray. Both the six sided tray and the seven sided tray provide a square corner around which a label can be wrapped so that it is visible from two adjacent sides of the tray. The seven sided tray can be formed from the same blank size as the standard eight sided package, and neither its machine nor manual assembly is any more complicated than the standard eight sided package. Further, the top to bottom compression resistance of the seven sided tray is 10% to 25% greater than a standard four sided tray.
In the six sided tray, the two diagonal corner panels not squared are lengthened approximately 30% as compared with a conventional eight sided tray of comparable size. The longer diagonal corner panels increase the top to bottom compression strength of the six sided tray so that it is about the same as a similar size eight sided tray. This compression performance of the six sided tray was unexpected. Moreover, better fit of the cover was obtained because of the two diagonally opposed square corners. Further, machine conversion from four sided to six sided is easier than from four sided to eight sided. The six sided tray may be adapted for either machine set up or manual set up.
The invention is a simple, economical and effective way to maintain stacking strength and improve resistance to distortion from force applied laterally to the sides or ends of trays having diagonal corner panels. Trays incorporating the invention, whether orienting the diagonal corner panels at 38xc2x0, or squaring at least one corner, or both, can be produced and generally handled with existing machinery.